1. Field of the Invention
The present invention relates to a Liquid-Crystal Display (LCD) device. More particularly, the invention relates to a LCD device formed by dripping a liquid crystal onto the lower substrate and by coupling it with the upper substrate with a sealing member, and a method of fabricating the device.
2. Description of the Related Art
As the methods of fabricating LCD devices, the “vacuum injection” method and the “dripping and coupling” method have been known so far.
With the “vacuum injection” method, a pair of substrates (i.e., the lower and upper substrates) are coupled together with a sealing member with an injection hole in such a way as to form a gap therebetween. The sealing member is formed by a thermosetting resin. Thereafter, the substrates thus coupled are subjected to heat treatment for curing the member, forming a vacant cell. Then, the inside of the cell is degassed and immersed into a desired liquid crystal. Thus, the liquid crystal is injected into the cell by way of the injection hole due to the pressure difference between the inside and outside of the cell. Finally, the injection hole is closed, resulting in the LCD cell.
On the other hand, with the “dripping and coupling” method, before a pair of substrates (i.e., the lower and upper substrates) are coupled together with a sealing member, a rectangular-frame-shaped sealing member is formed on the lower substrate and a desired liquid crystal is dripped onto the lower substrate inside the sealing member. The sealing member is formed by a ultraviolet (UV)-setting resin. Thereafter, the lower and upper substrates are coupled together with the sealing member and are subjected to UV light irradiation for curing the member, resulting in the LCD cell. The liquid crystal is filled In the cell at this state because it has been dripped onto the lower substrate in advance.
With the “vacuum injection” method, the liquid crystal is injected into the vacant cell due to the pressure difference and therefore, the following problems have occurred with the increasing size of LCD panels.
Specifically, when this method is applied to fabrication of a large-sized LCD panel, (i) the liquid crystal is difficult to reach the positions far away from the injection hole is desired, (ii) it takes a long time to complete the vacuum injection process of the liquid crystal, and (iii) display unevenness is likely to occur in the vicinity of the injection hole.
On the other hand, these problems (i) to (iii) can be solved in the “dripping and coupling” method and thus, this method has ever been used practically for fabricating large-sized LCD panels. However, the inventors found that this method has the following problems or disadvantages.
FIGS. 1 to 3 show the parts of the lower substrate of a typical LCD panel, respectively. FIG. 4 shows the cross-section along the line IV—IV in FIG. 3.
The surface of a lower substrate 1101 is divided into a rectangular display area 1401 located in the middle part, a rectangular-frame-shaped peripheral area 1402 located to surround the area 1401, and a terminal formation area 1403 located outside the area 1402. In the display area 1401, pixels 1109 are arranged in a matrix array. In the peripheral area 1402, a sealing member 1201, gate lines 1103, drain lines 1105, conductive light-blocking members 1106 are formed. In the terminal formation area 1403, gate terminals 1102, drain terminals 1104, and common terminals 1110 are formed.
The gate lines 1103 interconnect the pixels 1109 with the gate terminals 1102. The drain lines 1105 interconnect the pixels 1109 with the drain terminals 1104. The light-blocking members 1106 interconnect the common terminals 1110 with each other. The light-blocking members 1106 have the function of blocking or shielding the external light into the display area 1401 and the function of supplying the common voltage to the common electrode 1303 on the upper substrate 1301, as shown in FIG. 4. The sealing member 1201, which has a shape of rectangular frame, is formed to overlap with the gate and drain lines 1103 and 1105 and the light-blocking members 1106 in the peripheral area 1402.
The lower substrate 1101 is coupled with the upper substrate 1301 with the sealing member 1201 in such a way that a small gap is formed between the substrates 1101 and 1301, as clearly shown in FIG. 4. The liquid crystal layer 1203 is formed in the gap between the substrates 1101 and 1301. A dielectric layer 1107 is formed to cover the surface of the lower substrate 1101.
In the fabrication sequence of the LCD panel, UV light is irradiated to the sealing member 1201 after coupling the substrates 101 and 103, thereby curing the member 1201. In this process, as shown in FIG. 4, a UV exposure mask 1501 with a desired pattern 1502 is placed below the lower substrate 1101 at a specific gap and then, UV light is irradiated upward by way of the mask 1501. The inventors found that the sealing member 1201 does not receive the light as desired in this process, because the UV light is partially blocked by the light-blocking members 1106. Such insufficient irradiation of the UV light to the members 1201 leads to elution of some constituents of the UV-setting resin of the members 1201 into the liquid crystal layer 1203, resulting in defective quality. In particular, this problem will be conspicuous at the location where the light-blocking member 1106 extends along the sealing member 1201 in such a way as to overlap almost entirely with the member 1201, as shown in FIG. 3.
Moreover, the UV light irradiated to the sealing member 1201 is partially blocked by the light-blocking members 1106 and the gate and drain lines 1103 and 1105. Therefore, the irradiation quantity of the UV light to the sealing member 1201 is decreased near the members 1106 and the lines 1103 and 1105. In recent years, the intervals of the lines 1103 and 1105 tend to be narrower with the increasing size and resolution of LCD devices and thus, not only the members 1106 but also the lines 1103 and 1105 will apply more effect to the irradiation quantity. As a result, the irradiation quantity of the UV light to the member 1201 will fluctuate within a wider range from place to place in the near future. This leads to undesired non-uniform curing of the material of the member 1201.
If the light-blocking members 1106 are eliminated, the problem of non-uniform curing of the member 1201 can be almost solved. In this case, however, the common voltage is unable to be supplied to the opposite common electrode 1303 on the upper substrate 1301 and at the same time, external light is likely to enter the display area 1401 to thereby cause defective displaying operation. Thus elimination of the members 1106 is not realistic.